Re: [PATCH 3/2] padata: initialize usable masks to reflect offlined CPU

[Herbert Xu]

On Mon, Aug 12, 2019 at 05:02:00PM -0400, Daniel Jordan wrote:
> __padata_remove_cpu clears the offlined CPU from the usable masks after
> padata_alloc_pd has initialized pd->cpu, which means pd->cpu could be
> initialized to this CPU, causing padata to wait indefinitely for the
> next job in padata_get_next.
> 
> Make the usable masks reflect the offline CPU when they're established
> in padata_setup_cpumasks so pd->cpu is initialized properly.
> 
> Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> Cc: linux-crypto@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> 
> Hi, one more edge case.  All combinations of CPUs among
> parallel_cpumask, serial_cpumask, and CPU hotplug have now been tested
> in a 4-CPU VM, and an 8-CPU VM has run with random combinations of these
> settings for over an hour.
> 
>  kernel/padata.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)

If we modify patch 2/2 by calling this after cpu_online_mask
has been updated then this problem should go away because we
can then remove the cpumask_clear_cpu calls.

Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt